echo $variable | sed ....

a="hello world"
b="how are you"
c="best wish to you"
d="222,333,444"

# check if variable 'a' contains 'you'

if echo "$a" | grep -q you
then
   echo "Variable a contains 'you'"
fi

# Print variables values which contains 'you'

cat <<EOD | awk -v FS='=' '/you/'
$a
$b
$c
$d
EOD

# Print variables names of variables which contains 'you'

cat <<EOD | awk -v FS='=' '/you/ {print $1}'
a=$a
b=$b
c=$c
d=$d
EOD

a="hello world"
b="how are you"
c="best wish to you"
d="222,333,444"

# Replace 'you' by 'me' in variable b

b=$(echo "$b" | sed 's/you/me/')

# Replace 'you' by 'me' in variablesa b c d

b="how are you"
for var in a b c d
do
   eval value="\$$var"
   new_value=$(echo "$value" | sed 's/you/me/' )
   eval $var="\$new_value"
   # Can be done in one statement :
   # eval $var=\$\(echo "\$$var" \| sed 's/you/me/' \)
done

d="222,333,444"

# grep field 2 of variable d (seperator=,)

field2=$(echo "$d" | cut -d, -f2)